Inuyasha is roughly 150 years old when he first meets Kikyo and 200 years old when he meets Kagome.
The Staff of Heads, or nintoujou, wielded by Sesshoumaru's retainer Jaken is an actual artifact displayed at the Kamakura Museum in Japan.
After 167 episodes, Sunrise decided to end the animated show because it had caught up to the still-ongoing manga series it is based on and they were out of material. However, on a radio talk show, the producer of the show announced that they only ended the first series of the show, hinting that a second series will be coming soon. The series has since concluded with a 26 episode series titled Inuyasha Kanketsu-hen (2009) where all original voice actors, except for Kagome's voice actress Moneca Stori return for the conclusion. The anime concluded it's run on March 27, 2010.
Naraku is Japanese for "Hell".
Inuyasha's father is never mentioned by a proper name. His title, "The Great Dog General" would be spoken as "InuTaisho" in Japanese.